An injection-molding machine of this type has been disclosed, for example, in U.S. Pat. No. 3,224,043 to Lameris et al. There, two cavity plates on oppositely movable platens are provided for the molding of two-color workpieces. Another use of such a turret, namely as a temporary carrier for labels to be inserted into a mold cavity, is described in U.S. Pat. No. 4,213,204 to Edwards.
Even when both platens are movable in opposite directions, the turret should also be shiftable in the direction of platen motion in order to provide extra clearance, when necessary, and to adjust itself to different mold-closing strokes when plates of different thicknesses are being used; such slidability, of course, is essential when one platen is stationary. Thus, as shown in the patent to Lameris et al, the turret may have a shaft journaled at opposite ends in two blocks that are slidable on respective pairs of tie bars serving for the guidance of the platens. The mechanism for rotating the turret will therefore not be fixedly positioned and cannot be easily coupled with the clamp drive through a positive mechanical linkage. With electrical synchronization, on the other hand, malfunctions could result in a premature closure of the mold before arrival of the turret in its next operating position; conversely, rotation of the turret could be started before the mold is fully opened, i.e. when the platens have not been sufficiently withdrawn to avoid a destruction of the freshly molded workpieces or of the mold itself by such rotation.
In our copending and prior applications identified above, we have disclosed indexing means including coacting formations on a platen and on a workpiece-extracting member for positively locking the latter in an operating position during incipient relative movement of the platens into the mold-closed position. As specifically described in these earlier applications, the member so indexable is a take-off plate inserted between two complementary mold portions on the platens.